The present invention relates to tubular blind fasteners of the type that can be inserted through a preformed hole in a work piece and secured therein by a setting operation carried out from one side of such work piece. More particularly, this invention is directed to a blind fastener utilising a pull mandrel to effect the setting operation by compressing and deforming the tubular body of the fastener to compress such work piece between the deformed part of the body and a radially extending flange. There are numerous variants of such type of blind fastener, such as those generally known as a blind rivet, an example of which is such as that sold by the applicant under their registered trademark POP®.
Such blind rivets of standard sizes are heavily employed by many different industries and are hence manufactured in extremely large numbers, thereby minimising manufacturing costs and justifying investment in the expensive tooling required to manufacture such rivets.
Blind fasteners of this type provide an extremely effective and useful fastening component allowing connection to or securing of two or more work pieces, particularly where access is limited or restricted to one side of that work piece. This desirable trait is not limited to the commonly available sizes of blind rivet, but is equally applicable to specialised blind fasteners having larger length and/or diameters. In addition, specialised applications of such type of blind fasteners require fasteners utilising high performance and more intractable materials such as stainless steel. Other applications require fasteners made from higher strength materials and which are also required to be corrosion resistant, whereby the use of materials such as nickel/copper alloy are preferred. These non standard materials (as opposed to commonly used aluminium or steel), present specific difficulties in the manufacture of blind fasteners often necessitating compromise in the choice of material between its workability, strength and its corrosion resistance. In addition, to produce blind fasteners, particularly very large diameter blind fasteners specifically having a range of different lengths, is very expensive and time consuming, necessitating large and costly manufacturing machines and expensive tooling, the cost of which is often difficult to recoup due to the relatively low volumes required of such specialist blind fasteners. The volume of product required does not justify the expense of the manufacturing equipment. Even though many existing production machines have adequate forging load capacity, longer lengths of blind fastener may require larger machines since lengths of blind fastener often extends beyond the stroke capabilities of that particular machine. Additionally, different lengths of rivet require different sets of tooling for each length which further increases the cost of the manufacturing equipment and hence the product.
Additionally, where rivets are required for high performance and necessitate more intractable materials such as stainless steel, then the production of rivets from such material requires more robust and slower running production machines, such reductions in speed further increase manufacturing costs whereby the strength of the materials being used result in the associated production tools having a dramatically reduced life expectancy.
Still further, where it is desirable to produce a rivet requiring compromise between the choice of material in terms of its workability and its corrosion resistance, that there is a need for a material where the body portion of the rivet may different to that of the rivet head which, under conventional construction, would be impossible to achieve. This has lead to the development of very specialised types of blind fastener whereby the collar or flange portion is swaged on to a tubular rivet body.
This type of swaged collar type of blind fastener consists of essentially of a tubular rivet body with an integral swaging collar on a central setting mandrel. Such blind fasteners are extremely expensive to manufacture. In practice this type of fastener is applied by inserting the pulling portion of the setting mandrel into the pulling jaws of a conventional setting tool, while a shaped nose piece of the setting tool engages the swaging collar. As the pulling jaws retract, the blind side of the fastener collapses forming a characteristic blind side spread, whereby as the setting load further increases, the swaging collar is forced inwardly of the rivet body so that the collar material enters holding grooves of the setting mandrel. On completion of the setting operation, the setting load increases until the mandrel breaks at a predetermined point and load.
However, since the swaging collar and tubular body are in one piece, then any heat treatment applied to such fasteners is applied equally to both parts, making a compromise on their relative functions. For instance, a collar portion requires to be fully annealed so that it can be swaged with a relatively low load whereby the body portion may need to be partially annealed so it does not collapse prematurely and be overset before the deformation of the swaging collar has time to engage in the holding grooves on the pin.